1. Field of the Invention
The present invention relates to a thermal printer that performs printing on a sheet sandwiched between a thermal head and a platen roller, and more specifically to an attachment and detachment mechanism for a thermal head.
2. Description of the Related Art
Thermal printers are often employed as, for example, printers for performing receipt printing at cash registers, portable label printers for printing POS labels on food products or for printing labels for distribution control, or the like. In a thermal printer, a thermal head having a heat generating element is brought into press contact with a platen roller, with printing performed on a heat-sensitive recording sheet sandwiched between the two members.
In conventional thermal printers, for example, a thermal head is fixed to a head support member also serving as a heat radiation plate, and the head support member is axially supported to an outer frame or the like of the printer so as to be freely rotatable, with the head support member being urged by a spring or the like to be pressed toward the platen roller side (for example, see JP 2000-318260 A).
In such conventional thermal printers, when, for instance, defects develop in the print dots produced by the thermal printer due to the influence of excessive energization, damage on the sheet, etc., the only way to solve this problem is to dissemble the entire printer assembly to replace the thermal head, and such an operation is extremely troublesome.
In particular, in the conventional thermal printers, an E-shaped fastening fitting, namely the so-called E-ring, is fastened and secured to a shaft for axially supporting the head support member to the outer frame of the printer so that the shaft is securely fixed and does not slide sideways, or, alternatively, a support shaft provided so as to project from the either right and left side surface of the head support member is press-fitted to a bearing provided on the outer frame to be fixed in place. The above construction of the conventional printers makes it hard to detach the head support member with ease. Further, it is also impossible to detach only the thermal head portion while the head support member is incorporated in the printer main body as it is.
Generally speaking, in the case of thermal printers for printing letters or the like, a printing failure of a single dot does not really necessitate replacement of the thermal head. In recent years, however, label printers that perform label printing for delivery control are often used for barcode printing, and if, as anticipated, barcodes are to be printed in increasingly thinner lines in the future, even slight chipping or loss of dot may cause trouble. Hence, it is conceivable that replacement of the thermal head due to dot failures, etc. will become more frequent than was previously the case.
In view of the above, the inventors of the present invention have proposed a thermal printer which includes a lock arm that movably holds a head support member, an urging means suspended between the head support member and the lock arm and adapted to generate a pressing force between a thermal head and a platen roller, and an outer frame that holds the lock arm and the platen roller, in which the thermal head, the head support member, and the urging means are capable of being attached to and detached from the outer frame while being assembled onto the lock arm (JP 2002-283230 B). With the thermal printer, the thermal head portion can be readily removed from the printer main body, facilitating replacement of the thermal head portion.
In the thermal printer proposed in the above previously filed patent application, however, the thermal head, the head support member, and the urging means are assembled onto the lock arm, which means that when replacing the thermal head, it is also necessary to replace the head support member, the urging means, and the like together with the thermal head, leading to an increase in parts cost. Conceivably, an improvement in this respect will enable a further reduction in maintenance cost.
It is an object of the present invention to provide a thermal printer which provides ease of maintenance, such as ease of replacement of the thermal head, and which can shorten the time required for maintenance work and reduce maintenance cost.